Project Summary Limb amputation is a devastating event with an associated loss of every day function coupled with a dramatic change of life. In the United States alone, 1.6 million people have lost a limb -- nearly 1 in every 200 people. Of these cases, 846,000 limbs (54%) were lost due to dysvascular diseases (diabetes), 705,000 limbs (45%) were lost due to traumas, and 18,000 (1%) limbs were lost due to cancer. Unfortunately, over the next generation, these numbers will only increase. Projections anticipate by the year 2030, the prevalence of diabetes in the United States will nearly double, and will triple by the year 2050. Furthermore, locally within the United States, high-energy motor vehicle collisions and all-terrain vehicle accidents are the top contributors to the number of limbs amputated due to traumas. Abroad, the advancements in battlefield medicines and technologies such as body-armor have saved more combatants than ever before. Unfortunately, there is not adequate protection for the extremities and many US veterans are returning from combat with traumatic amputations that require follow-up care, extensive rehabilitation, and expensive prosthetic services from the Veterans Administration healthcare programs. According to the Army Office of the Surgeon General, between September 2001 and January 12, 2009, there were 1,286 limbs amputated in Operation Iraqi Freedom, Operation Enduring Freedom, and unaffiliated conflicts, of whom nearly 70% have suffered major limb amputations. Many patients can use an exoprosthesis (prosthetic device outside the body) to partially replace their missing extremity. These patients currently have the ability to attach, or to dock, the exoprosthetic limbs to the soft-tissues of their residual limb. However, nearly 60% of the 270,000 patients with amputations of the upper extremity reject the use of exoprostheses because of issues such as poor fit, difficulties with training, limited usefulness, and short residual limb-lengths. It is for these patients that a new approach to designing percutaneous, osseointegrated endoprostheses is needed to meet the needs of these deserving patients. The purpose of this project is to develop a method to predict the mechanical stability of osseointegrated, percutaneous endoprostheses proposed for above elbow amputees. We will design a series of straight-stemmed endoprostheses and anatomical-stemmed endoprostheses to fit a sampling of human humeri with varying residual limb- lengths, comparing the initial bone morphology of (a) the cortical thickness of the host bone prior to implantation, (b) the mineral content of the host bone prior to implantation, (c) the percent contact between the endoprostheses and the host bone following implantation, and (d) the percent bone loss resulting from implantation. Next, we will mechanically test the straight-stemmed and anatomical-stemmed endoprostheses implanted in-situ in the humeri, analyzing (a) the amount of implant loosening, (b) the number of cycles to failure, and (c) the load to failure required in both tension/compression and anteroposterior bending. Then, we will be able to develop equations to predict the skeletal stability of endoprostheses for above elbow amputees using correlations between the initial bone morphology with the mechanical stability following implantation. Fundamentals developed from this project will allow for a thorough versatile extension of the strategy to future endoprostheses used for below-knee, above-knee, above-elbow, below-elbow amputees, and digit amputees.